1. Field of the Invention
The invention relates to an apparatus for testing a semiconductor wafer, and also to a contact film to be used for such an apparatus.
2. Description of the Related Art
Hereinbelow will be explained a method of testing a DRAM semiconductor wafer by using a memory tester as an example of a conventional test for a semiconductor wafer with reference to FIG. 1 illustrating a conventional tester including a wafer prober.
A tester includes a wafer prober 10 having a generally U-shaped frame 11. On a lower inner surface of the U-shaped frame 11 is placed an X-Y stage 12 capable of moving in two directions perpendicular to each other. On the X-Y stage 12 is placed a vacuum chuck 13 for fixing a wafer 14 to be tested thereon in place. To an upper inner surface of the U-shaped frame 11 is secured a probe card 15 from which probes 16 extend vertically downwardly. The probes 16 are to make electrical contact with contact pads formed on an upper surface of the wafer 14 to be tested. The tester further includes a memory tester 17 which is in electrical connection with the wafer prober 10 through a cable 18.
The memory tester 17 provides electrical power and signals required for carrying out a test to the wafer 14 to be tested through the cable 18 and the probe card 15, whereas the wafer 14 transmits output signals to the memory tester 17 through the probe card 15 and the cable 18. The memory tester 17 analyzes the thus received output signals, and judges as to whether the wafer 14 operates properly or not.
However, the probes 16 can make contact with only the limited number of pins due to, for instance, the limited number of pin electronics cards of the memory tester 17. Hence, in general, at greatest 8 chips among chips mounted on the wafer 14 to be tested are concurrently tested, and then the wafer 14 is moved by the X-Y stage 12 to thereby test next 8 chips.
Japanese Unexamined Patent Publication No. 2-239641 published on Sep. 21,1990 has suggested another apparatus for probing a semiconductor wafer. The suggested apparatus comprises a box type test head including a test circuit therein, a performance board mounted on top of the test head, a connector secured to the test head for connecting the test circuit to the performance board, a fixed card mounted on the performance board in electrical connection therewith, and a semiconductor chip to be tested which is to make contact with a fixed probe mounted on the fixed card. This apparatus is characterized by that signals for measuring semiconductor pellet performance are caused to run between the performance board and the fixed card.
The conventional testers as mentioned above have problems such as that they can test only the limited number of chips at a time and hence it takes much time to test all chips mounted on a wafer to be tested, and that they cannot carry out high frequency test because of long wiring distance between the tester and the memory tester.
Turning to a film to be used for a semiconductor wafer probing apparatus, there has been suggested a ultra-high density anisotropic conductive film by Masakazu Sugimoto et al. in Nitto Technical Report, Vol. 30, No. 1, May 1992, pp. 45-47. A conventional film including the above mentioned film has no resiliency in a film-width direction, resulting in that it is quite difficult to carry out a plurality of contacts at a quite small pitch at a time in a wide area.